Project Summary/Abstract This proposal encompasses a research and training plan that will transition Dr. Huang from a mentored role to an independent investigator. Dr. Huang recently completed his hematology/oncology fellowship at the University of Pennsylvania, and is currently an Instructor of Medicine in the Division of Hematology/Oncology. His long-term goal is to establish an independent R01 funded lab focusing on mechanisms of response and resistance to cancer immunotherapies. His short-term goals, that will be facilitated through the K08, include gaining technical expertise in tumor whole exome sequencing, neoepitope prediction, and transcriptomics. In addition, he seeks to gain proficiency in big data analysis, clinical trial design, and biostatistics. Dr. Huang has chosen Dr. E. John Wherry as his primary mentor and Dr. Tara Michell as his co-mentor. Dr. Wherry is a world leader in in CD8 T cell biology, including transcriptomics of CD8 T cell exhaustion and Dr. Mitchell is a melanoma clinical trialist and a leader of Penn's melanoma research program. In addition, he has assembled a strong and complementary mentoring committee composed of basic scientists, physician-scientists, and a biostatistician to support him in his research direction and career development. Dr. Huang has recently published in Nature that anti-PD-1 therapy reinvigorated exhausted CD8 T cells (TEX), that could be identified in the peripheral blood of melanoma patients. The magnitude of this immune response generated by anti-PD-1 therapy was proportional to the overall tumor burden of the patient, as measured by the sum of the long diameter of all of the patient's tumors. Yet, patients with a large burden of tumor have a poor outcome with anti-PD-1 therapy despite the generation of a large immune response. The proposed research focuses on why a large immune response generated by anti-PD-1 therapy is not sufficient to control a large tumor burden. Dr. Huang hypothesizes that that high tumor burden is associated with a quantitative and qualitative defect in the melanoma-specific immune response generated by anti-PD-1. Thus, he will test whether high tumor burden is associated with 1) a decreased magnitude and persistence of melanoma-specific immune response (Aim1), and 2) a defect in differentiation from TEX to functional memory T cells (TMEM) (Aim2). Dr. Huang will take advantage of an innovative clinical trial of neo-adjuvant (pre-surgical) anti-PD-1 therapy in melanoma with availability of blood samples before and after anti-PD-1, and after tumor resection. These studies will advance the field of cancer immunotherapy by elucidating the role of high tumor burden in limiting T cell reinvigoration, and establish the rationale for therapeutic interventions to reduce tumor burden, such as surgical debulking. The mentorship and training provided will effectively transition Dr. Huang to an independent research career studying the mechanisms of immunotherapy response and resistance in the context of novel clinical trials.